: Well, maybe. The American Heritage Dictionary says "root" in the sense of applause, encouragement, etc., is "perhaps from ROOT to dig with the snout." In the Oxford English Dictionary, that sense is listed in the entry for "root" that includes digging with the snout; it is labeled U.S. slang and is said to have appeared in another dictionary in 1985. The dictionaries don't explain how shouting and waving your arms is like poking around for truffles.

Collins English Dictionary says:
to give support to ......[C19: perhaps a variant of Scottish 'rout' - to make a loud noise, from Old Norse 'rauta' to roar.